If you need custom entity data from Dynamics to be available in Marketo, here's how to enable the sync for it:
Admin Permissions Required
1. Go to the Admin section.
2. Select Microsoft Dynamics and click Disable Sync.
You must disable the global sync temporarily in order to enable or disable a custom entity.
3. Under Database Management, click the Dynamics Entities Sync link.
4. Click the Sync schema link.
5. Select the entity you want to sync and click Enable Sync.
6. Select the fields you want to sync or use as constraints and/or triggers in smart lists. When done, click Enable Sync.
7. The entity now has a green checkmark on it.
8. Don't forget to re-enable the global sync!
Oh yeah! Powerful stuff.